For precise window measurements, it is essential to measure from the exterior brickwork opening of the property, utilizing millimetres (mm) as the standard unit.
Commence by measuring the width from brickwork to brickwork at three distinct locations (top, middle, and bottom) and subsequently deduct approximately 10mm from the smallest measurement recorded.
Following that, accurately measure the height of the opening at multiple locations and subtract approximately 10mm from the smallest measurement obtained. In instances where a metal lintel is present, please exclude it from your calculations. Typically, windows are installed on a cill; therefore, measure from the underside of the existing cill unless it is a non-removable feature, such as stone.